Study On The Influence Of Crankshaft Torsional Vibration On Noise Performance Of Engine

As the core component of engines,vibration of crankshaft system has an important impact on the NVH performance of engines and vehicles.In this paper,the influence of crankshaft elastic vibration on the vibration and radiated noise of engine block was studied firstly.The results show that crankshaft elastic vibration will increase the amplitude of vibration velocity and radiated sound power.However,the amplitude change of the axial vibration is more obvious than that of the transverse and vertical vibration.Torsional vibration of the crankshaft system has always been an important branch in the realm of internal combustion engine research.In this paper,CAE technique was used to calculate forced torsional vibration response of crankshaft system,and the torsional vibration characteristics were analyzed.The effect of main parameters on performance of TVD was studied in theory.Aiming at rubber TVD,the impacts of torsional stiffness of rubber layer and MOI(Moment of Inertia)of inertia ring on vibration amplitude of main harmonics were calculated.The results show that the impacts of these parameters on amplitudes of different main harmonics are similar.As the torsional stiffness of the rubber layer decreases(or the MOI of inertia ring increases),the vibration amplitude corresponding to the lower speed region decreases,while the vibration amplitude corresponding to the high speed region increases.Moreover,compared with changing torsional stiffness of the rubber layer,the reduction of torsional vibration amplitude is more obvious when the MOI of inertia ring is changed.And the conclusions were verified by experiments about TVD performance.Aiming at the abnormal noise in a passenger car at accelerating condition,comprehensive vibration and noise tests were launched.It was concluded that the frequency of abnormal noise was consistent with that of the first order torsional mode about crankshaft.In order to find out the relationship between abnormal noise and torsional vibration,CAE technique was used to calculate forces and pressure distribution of main bearings at the cases of with TVD and without TVD(steel wheel).Also,additional forces caused by torsional vibration on engine block were researched.And,the mechanism of abnormal noise caused by crankshaft torsional vibration was explored.The results show that torsional vibration will increase the amplitude of the exciting force on the engine block.This change is more obvious in frequency domain(near 400 Hz).The effect of torsional vibration to the transverse excitation on block is more significant.In addition,torsional vibration will influence the amplitude and distribution of pressure on surface of main bearings,which may cause damage to the oil film and change the lubrication state of bearings,and then will result in abnormal noise.To improve the abnormal noise caused by torsional vibration,optimization on original TVD was launched.With the optimized TVD,noise tests and subjective evaluation found that the abnormal noise decreased significantly,which had met the demand of consumers.The results of torsional vibration measurements show that the amplitude of total and main harmonic vibration of the crankshaft(order8 and order10)reduced obviously.The conclusions of simulations are verified by the results of experiments to some extent.